SOCKS5 authentication with OkHTTP fails

Question

I'm trying to get SOCKS5 proxy working with authentication in OkHTTP.

Authentication works fine for HTTP proxies using the following code:

proxy = new Proxy(Proxy.Type.HTTP, new InetSocketAddress("host", 1000));

Authenticator proxyAuthenticator = new Authenticator() {
    @Override
    public Request authenticate(Route route, Response response) throws IOException {
        String credential = Credentials.basic("username", "password");
        return response.request().newBuilder()
                                 .header("Proxy-Authorization", credential)
                                 .build();
        }
    };

    client = defaultClient(key, timeout)
        .newBuilder()
        .proxyAuthenticator(proxyAuthenticator)
        .proxy(proxy)
        .build();
}

But when using Proxy.Type.SOCKS it throws java.net.SocketException: SOCKS : authentication failed.

I've found a few SO (1, 2) and GitHub answers on the topic but none have a working code example.